The present invention relates to an injection moulding process, more particularly to a process for manufacturing injection moulded objects of thermoplastic material, to a device for carrying out such processes, and to a new type of moulded objects obtainable with such process.
Injection moulding of thermoplastic materials to produce objects of all sorts of shapes and sizes, is well known in the art.
It is also known however that there are certain limitations to the size of the objects to be moulded (in function also of the complexity of the moulded shapes) as a consequence of the rheologic properties of the molten thermoplastic in the moulds.
As the flow of molten plastic progresses into the mould cavity the material will cool down, which together with the rheological resistances in the mould will cause the pressure to build up at the point of injection; these pressures will of course be related to the length of the flowlines in the mould and therefore to the size of the object to be moulded.
To overcome these problems several solutions have been proposed in the art, such as:
high pressure equipment to overcome the pressure build-up, but this approach is quite expensive due to the material costs involved; PA1 use of heated moulds to avoid the cooling down of the molten plastic in the mould, but this approach is also complex and costly due to the structural complexity of the different parts of such a heated mould; PA1 use of a plurality of injection points into the mould cavity to increase the speed of injection and the volume of the molten material flowing into the mould so as to reach the other side of the mould and fill the mould before the pressure builds up too much, but this approach has only shown satisfactory where the size of the object to be moulded in the direction(s) away from the injection points (the "second dimension" or base area, and the "third dimension" or height of the three dimensional object) is still relatively limited, i.e. at most about 50-60 cm, and at the absolute most about 80 cm when also using high pressure technology and/or heated mould technology and/or very special thermoplastics.
The object of the present invention is to provide a method for manufacturing injection moulded objects of thermoplastic material which overcomes the drawbacks of the known art and which in particular allows the injection moulding of objects having a size of more than 80 cm in a direction away from the injection point(s), or objects having a size of more than 60 cm in a direction away from the injection point(s) without using high pressure technology. It is also the object of this invention to provide a possibility for objects having a size of more than 80 cm along each of its three dimensional axes.